Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C19/00—Acyclic saturated compounds containing halogen atoms
  • C07C19/08—Acyclic saturated compounds containing halogen atoms containing fluorine
  • C07C19/10—Acyclic saturated compounds containing halogen atoms containing fluorine and chlorine
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/093—Preparation of halogenated hydrocarbons by replacement by halogens
  • C07C17/20—Preparation of halogenated hydrocarbons by replacement by halogens of halogen atoms by other halogen atoms
  • C07C17/202—Preparation of halogenated hydrocarbons by replacement by halogens of halogen atoms by other halogen atoms two or more compounds being involved in the reaction
  • C07C17/206—Preparation of halogenated hydrocarbons by replacement by halogens of halogen atoms by other halogen atoms two or more compounds being involved in the reaction the other compound being HX

Definitions

• This invention relates to the production of halocarbons and their azeotropes and more particularly to the production of difluoromethane (i.e., CH2F2 or HFC-32) and azeotropes of chlorine-containing precursors thereof (i.e., CH2CIF or HCFC-31, and CH2CI2) with HF.
• difluoromethane i.e., CH2F2 or HFC-32
• azeotropes of chlorine-containing precursors thereof i.e., CH2CIF or HCFC-31, and CH2CI2 with HF.
• Chlorofluorocarbons are compounds containing only carbon, fluorine and chlorine.
• CFCs have been used for many years as refrigerants, heat transfer media, foam expansion agents, aerosol propellants, solvents and power cycle working fluids.
• CFCs may be detrimental to the Earth's ozone layer. Consequently, there is a worldwide effort to find alternative compounds which contain fewer or preferably no chlorine substituents.
• the hydrofluorocarbon difluoromethane has been proposed as a replacement for some CFCs, particularly, in refrigeration, air-conditioning and other applications (see e.g., European Patent Application Publication No. 508,660 Al) . Accordingly, there is interest in developing efficient processes for the production of HFC-32.
• Japanese Patent Publication 59-225131 discloses preparation of HFC-32 by reacting dichloro ethane with HF in the vapor phase at 200 to 500°C in the presence of a catalyst which consists of chromium fluoride or which has been obtained by molding a mixture of chromium fluoride and a carrier or by supporting chromium fluoride on a carrier. Chromium fluoride may be obtained by fluorinating a chromium-containing compound. Immersion of activated carbon in a solution of chromium chloride, followed by treatment with HF is disclosed (see e.g., Example 2) . It is well known that activated carbon typically has an ash content comprising etal- containing compounds (e.g. .
• 1, 1-Dichlorotetrafluoroethane i.e., CCI 2 FCF3 or CFC-114a
• CCI 2 FCF3 or CFC-114a 1, 1, 1,2-tetrafluoroethane
• CF3CH2F can be obtained by the catalytic hydrogenolysis of CCI2FCF3 using a supported metal hydrogenation catalyst (see e.g., C. Gervasutti et al., J. Fluorine Chem., 1981/82, 19, pgs. 1-20) .
• a supported metal hydrogenation catalyst see e.g., C. Gervasutti et al., J. Fluorine Chem., 1981/82, 19, pgs. 1-20
• HFC-134a is an environmentally acceptable potential replacement for CFC refrigerants, blowing agents, aerosol propellants and sterilants that are implicated in the destruction of stratospheric ozone.
• the present invention provides a process for producing difluoromethane.
• the process comprises the step of contacting a gaseous mixture containing CH 2 CI2 and hydrogen fluoride with a catalyst containing a catalytically effective amount of trivalent chromium supported on a carbon having an ash content of less than 0.5 percent by weight, at a temperature of from about 180°C to about 375°C.
• the catalyst and temperature conditions of this process allow the concurrent reaction of 1, 1, 1-trichlorotrifluoroethane (i.e., CCI 3 CF3 or CFC-113a) with HF to form CFC-114a.
• CH2CIF and unreacted CH2CI2 each of which may be recovered as an azeotrope with HF, may be recycled.
• the present invention also provides compositions which consist essentially of hydrogen fluoride in combination with an effective amount of a compound selected from the group consisting of CH 2 CI 2 and CH 2 CIF to form an azeotrope or azeotrope-like composition with hydrogen fluoride, said composition containing from about 5 to 29 mole% CH 2 CI 2. or from about 58 to 65 mole% CH 2 CIF.
• the present invention provides a process for the vapor-phase catalytic fluorination of CH 2 CI 2 to CH 2 F 2 .
• the process may be used for the vapor-phase catalytic fluorination of mixtures of CH 2 CI 2 and CCI 3 CF 3 to produce both CH2F 2 and CCI 2 FCF 3 .
• the process of this invention employs catalyst compositions comprising trivalent chromium.
• trivalent chromium such fluorination catalysts can include other components to increase catalyst activity and/or life such as one or more divalent metal cations (e.g., zinc, magnesium and/or cobalt).
• trivalent chromium catalysts e.g., Cr 2 ⁇ 3
• trivalent chromium catalysts supported on non-carbon supports e.g., on alumina, aluminum fluoride, or magnesium fluoride
• this invention advantageously involves trivalent chromium (e.g., CrCl 3 and/or CrF 3 ) supported on a carbon which has an ash content of less than 0.5 weight percent.
• a CrF 3 on carbon is disclosed in U.S. Patent No. 3,632,834, the contents of which are incorporated herein by reference.
• Catalysts suitable for use in the process of this invention can be prepared in a manner similar to that disclosed in U.S. Patent No. 3,632,834, provided the carbon used has an ash content of less than 0.5 weight percent.
• Preferred catalysts include a low ash content carbon support (as described herein) containing chromium chloride (CrCl 3 ) , fluorided chromium chloride (e.g., CrCl 3 treated with HF to produce chromium chlorofluoride (s) ) , or mixtures of chromium chloride and chromium fluoride (CrF3) .
• a preferred carbon support is acid- 5 washing activated carbon prior to impregnating it with trivalent chromium.
• the chromium content (expressed as CrCl3) is from about 5 to 60 weight percent of the carbon supported catalyst.
• the initial acid treatment typically uses an acid
• acids used for the acid treatment contain neither phosphorus nor sulfur.
• acids which may be used in the initial acid wash during the catalyst preparation process include organic acids such as acetic acid and
• inorganic acids such as hydrochloric acid or nitric acid.
• hydrochloric acid or nitric acid is used.
• the second acid treatment when employed, advantageously uses hydrofluoric acid.
• the carbon is treated with acid such that after such
• the carbon contains less than about 0.2% by weight ash.
• carbons which may be treated with acids to provide suitable supports include those sold under the following trademarks: DarcoTM, NucharTM,
• the carbon support can be in the form of powder, granules, or pellets, etc.
• the acid treatment may be accomplished in several directions.
• a suitable procedure is as follows .
• a carbon support is soaked overnight with gentle stirring in a 1 molar solution of the acid prepared in deionized water.
• the carbon support is then separated and washed with deionized water until the pH of the washings is
• the carbon support is then soaked again with gentle stirring in a 1 molar solution of the acid prepared in deionized water for 12 to 24 hours.
• the carbon support is then finally washed with deionized water until the washings are substantially free of the anion of the acid (e.g., Cl ⁇ or NO 3 * ") , when tested by standard procedures.
• the carbon support is then separated and dried at about 120°C.
• the washed carbon is then soaked, if necessary, in 1 molar HF prepared in deionized water for about 48 hours at room temperature with occasional stirring.
• the carbon support is separated and washed repeatedly with deionized water until the pH of the washings is greater than 4.
• the carbon support is then dried followed by calcination at 300°C for about 3 hours in air prior to its use as a support.
• U.S. Patent No. 5,136,113 for further details relating to producing acid-washed carbon catalysts.
• the starting material to be fluorinated consists essentially of CH 2 CI 2
• the starting material to be fluorinated consists essentially of a mixture of CH2CI 2 and CCI 3 CF 3
• the molar ratio of HF added to the total amount of CH 2 CI 2 and CCI 3 CF 3 starting material added typically ranges from about 0.5:1 to about 10:1, and is preferably from about 1:1 to 8:1.
• the molar ratio of CH 2 CI 2 to CCI 3 CF 3 in mixtures ranges from about 1:9 to about 9:1.
• Suitable reaction temperatures range from about 180°C to about 375°C. Preferably, the reaction temperature is in the range of from about 200°C to about 350°C. Pressure is not critical. Atmospheric and superatmospheric pressures (e.g., from about 100 kPa to about 7000 kPa) are the most convenient and are therefore preferred.
• the fluorination reaction is performed in the vapor phase using well known chemical engineering practice, which includes continuous, semi-continuous or batch operations.
• the fluorination reaction may be done in the presence of inert gases e.g., nitrogen, helium or argo .
• the reaction product stream can be treated in accordance with any of the techniques known to the art for separating the desired fluorination product from by-product hydrogen chloride, unreacted hydrogen fluoride, chlorofluoromethane and other minor by-products.
• HFC-32 can be separated from the other components of the reaction products by distillation.
• chlorofluoromethane i.e., CH 2 CIF or HCFC-31
• CH 2 CIF and unreacted CH 2 CI 2 can each be recovered as a composition consisting essentially of an azeotrope thereof and HF, using distillation. Further discussion of these azeotropes is provided below.
• the product stream may be scrubbed with water or aqueous alkali to remove hydrogen halides, dried with a drying agent, such as silica gel or a molecular sieve adapted to such purpose and recovered.
• a drying agent such as silica gel or a molecular sieve adapted to such purpose and recovered.
• CH 2 CIF and unreacted CH 2 CI 2 and/or their azeotropes with hydrogen fluoride are recycled to the fluorination reactor.
• the reactors, separators and their associated feed lines, effluent line and associated units should be constructed of materials resistant to hydrogen fluoride, hydrogen chloride and chlorine.
• Typical materials of construction include stainless steels, in particular of the austentic type, and the well-known high nickel alloys, such as Monel® nickel-copper alloys, Hastelloy® nickel-based alloys and, Inconel ® nickel-chromium alloys.
• Also suitable for reactor fabrication are such polymeric plastics as polytrifluorochloroethylene and polytetrafluoroethylene, generally used as linings.
• the present invention provides a composition which consists essentially of hydrogen fluoride and an effective amount of a compound selected from the group consisting of CH 2 CI 2 and CH 2 CIF to form an azeotropic composition with hydrogen fluoride.
• effective amount is meant an amount which, when combined with HF, results in the formation of an azeotrope or azeotrope-like mixture.
• an azeotrope or an azeotrope-like composition is an admixture of two or more different components which, when in liquid form under given pressure, will boil at a substantially constant temperature, which temperature may be higher or lower than the boiling temperatures of the components, and which will provide a vapor composition essentially identical to the liquid composition undergoing boiling.
• azeotrope-like composition means a composition that behaves like an azeotrope (i.e., has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation) .
• the composition of the vapor formed during boiling or evaporation is the same as or substantially the same as the original liquid composition.
• the liquid composition if it changes at all, changes only to a minimal or negligible extent. This is to be contrasted with non-azeotrope-like compositions in which during boiling or evaporation, the liquid composition changes to a substantial degree.
• the essential features of an azeotrope or an azeotrope-like composition are that at a given pressure, the boiling point of the liquid composition is fixed and that the composition of the vapor above the boiling composition is essentially that of the boiling liquid composition (i.e., no fractionation of the components of the liquid composition takes place) . It is also recognized in the art that both the boiling point and the weight percentages of each component of the azeotropic composition may change when the azeotrope or azeotrope-like liquid composition is subjected to boiling at different pressures.
• an azeotrope or an azeotrope-like composition may be defined in terms of the unique relationship that exists among components or in terms of the compositional ranges of the components or in terms of exact weight percentages of each component of the composition characterized by a fixed boiling point at a specified pressure. It is also recognized in the art that various azeotropic compositions (including their boiling points at particular pressures) may be calculated (see, e.g., W. Schotte Ind. Eng. ' Chem. Process Des. Dev. 1980, 19, pp. 432-439) . Experimental identification of azeotropic compositions involving the same components may be used to confirm the accuracy of such calculations and/or to modify the calculations at the same or other temperatures and pressures.
• compositions may be formed which consist essentially of azeotropic combinations of hydrogen fluoride with a compound selected from the group consisting of CH2CI 2 and CH 2 CIF. These include a composition consisting essentially of from about 42 to about 35 mole percent HF and from about 58 to about 65 mole percent CH 2 CIF (which form an azeotrope boiling at a temperature from about -25°C to about 75°C and a pressure between about 55 kPa and about 1700 kPa) ; and a composition consisting essentially of from about 95 to about 71 mole percent HF and from about 5 to about 29 mole percent CH 2 CI 2 (which form an azeotrope boiling at a temperature from about -50°C to about 110°C and a pressure between about 5 kPa and about 2280 kPa) .
• PTx Method To determine the relative volatility of HF with CH 2 CI 2 and with CH 2 CIF, the so-called PTx Method was used. In this procedure, the total absolute pressure in a cell of known volume is measured at a constant temperature for various known binary compositions. Use of the PTx Method is described in greater detail in "Phase Equilibrium in Process Design", Wiley- Interscience Publisher, 1970, written by Harold R. Null, on pages 124 to 126, the entire disclosure of which is hereby incorporated by reference. Samples of the vapor and liquid were obtained and analyzed to verify their respective compositions.
• an activity coefficient equation model such as the Non-Random, Two- Liquid (NRTL) equation
• NRTL equation Use of an activity coefficient equation, such as the NRTL equation, is described in greater detail in "The Properties of Gases and Liquids", 4th Edition, publisher McGraw Hill, written by Reid, Prausnitz and Poling, on pages 241 to 387; and in “Phase Equilibria in Chemical Engineering", published by Butterworth Publishers, 1985, written by Stanley M. Walas, pages 165 to 244; the entire disclosure of each of the previously identified references are hereby incorporated by reference.
• the NRTL equation can sufficiently predict whether or not mixtures of HF and either CH2CI 2 or CH 2 CIF behave in an ideal manner, and can sufficiently predict the relative volatilities of the components in such mixtures.
• the relative volatility approaches 1.0 defines the system as forming a near-azeotrope.
• the relative volatility is 1.0 defines the system as forming an azeotrope. It has been found that azeotropes of HCFC-31 and HF are formed at a variety of temperatures and pressures.
• azeotropic compositions consisting essentially of HCFC-31 and HF range from about 42 mole percent HF (and 58 mole percent HCFC-31) to about 35 mole percent HF (and 65 mole percent HCFC-31) .
• An azeotrope of HF and CH 2 CIF has been found at 20°C and 49.3 psia (340 kPa) consisting essentially of 37.5 mole percent HF and 62.5 mole percent CH 2 CIF.
• an azeotropic composition of about 42 mole percent HF and 58 mole percent HCFC-31 can be formed at -25°C and 55 kPa and an azeotropic composition of about 35 mole percent HF and 65 mole percent HCFC-31 can be formed at 75°C and 1700 kPa.
• the present invention provides an azeotrope or azeotrope-like composition consisting essentially of from about 42 to about 35 mole percent HF and from about 58 to 65 mole percent CH2C1F, said composition having a boiling point from about -25°C at 55 kPa to about 75°C at 1700 kPa.
• azeotropes of CH2CI2 and HF are formed at a variety of temperatures and pressures . Between 5 kPa (at a temperature of -50°C) and 2280 kPa (at a temperature of 110°C) azeotropic compositions consisting essentially of CH2CI2 and HF range from about 95 mole percent HF (and 5 mole percent CH 2 CI 2 ) to about 71 mole percent HF (and 29 mole percent CH 2 CI 2 ) .
• An azeotrope of HF and CH 2 CI2 has been found at 20°C and 20.8 psia (143 kPa) consisting essentially of 85 mole percent HF and 15 mole percent CH2CI2• Based upon the above findings, it has been calculated that an azeotropic composition of about 95 mole percent HF and 5 mole percent CH 2 CI 2 can be formed at -50°C and 5 kPa and an azeotropic composition of about 71 mole percent HF and 29 mole percent CH 2 CI 2 can be formed at 110°C and 2280 kPa.
• the present invention provides an azeotrope or azeotrope-like composition consisting essentially of from about 95 to about 71 mole percent HF and from about 5 to 29 mole percent CH 2 CI 2 , said composition having a boiling point from about -50°C at 5 kPa to about 110°C at 2280 kPa.
• azeotropes are considered to be heterogeneous in that two liquid phases are present.
• distillation including azeotropes with HF can typically be run under more convenient conditions than distillation without HF (e.g., where HF is removed prior to distillation) .
• a 5/8" (1.58 cm) I.D. Inconel® nickel alloy reactor was charged with a catalyst and heated to 300°C in a flow of nitrogen (25 mL/min) for about 20 hours. The temperature was reduced to 175°C and a 2:1 molar ratio of nitrogen and HF was started through the reactor (total flow 100 mL/min) . After one hour under these conditions, the molar ratio of nitrogen to HF was adjusted to 1:3 and the temperature increased gradually over a two hour period to 400°C. The reactor was then brought back to the desired operating temperature, the nitrogen flow stopped, and the flow of reactants started. Analytical Procedure
• the reactor effluent was sampled on-line at various run times (R.T.s) with a Hewlett Packard HP 5890 gas chromatograph using a 20 foot (6.1 m) long, one-eighth inch (0.32 cm) diameter, column containing KrytoxTM perfluorinated polyether on an inert support and a helium flow of 35 mL/min. Gas chromatographic conditions were 70°C for three minutes followed by temperature programming to 180°C at a rate of 6°C/minute. The table percentages are in area % unless noted otherwise. Carbons Used
• Carbon A a 6 x 16 mesh (about 3.4 mm x 1.2 mm) commercial grade coconut shell carbon which had (before washing) an ash content of about 2.3 weight percent; or Carbon B, a 4 x 8 mesh
• Carbon B had an ash content of less than about 0.1 weight percent.
• the reactor was charged with a 6% CrCl 3 on HC1- washed coconut Carbon A (30 mL, 14.7 g) catalyst and the catalyst was activated according to the Activation Procedure above.
• the reaction temperature was varied from 200 to 275°C, the molar ratio of HF to CH 2 CI 2 was 13
• reaction effluent was analyzed according to the Analytical Procedure above, The reaction results are shown in Table 1.
• the reactor was charged with a 7.5% CrCl 3 on HC1- washed Carbon B (15 mL, 6.22 g) catalyst and the catalyst was activated according to the Activation Procedure above.
• the reaction temperature was varied from 200 to 275°C
• the molar ratio of HF to halocarbon feed was varied from 2:1 to 6:1
• the contact time (C.T.) was varied from 2 to 30 seconds.
• the halocarbon feed consisted of 98.7 mole percent CH 2 CI 2 and 1.3 mole percent CH 2 CIF.
• the reaction effluent was analyzed according to the Analytical Procedure above. The reaction results, in mole percent, are shown in Table 2, 14
• the reactor was charged with a 7.5% CrCl 3 on Carbon A (15 mL, 6.4 g) catalyst, which was not acid- washed.
• the catalyst was then activated according to the Activation Procedure above.
• the reaction temperature was varied from 200 to 275°C, the molar ratio of HF to CH 2 CI 2 was varied from 2:1 to 4:1 and the contact time was 15 seconds in all cases.
• the CH 2 CI 2 feed to the reactor contained 98.9% CH 2 CI 2 and 1.1% CH 2 CIF.
• the reaction effluent was analyzed according to the Analytical Procedure above. The reaction results are shown in Table A. Comparison of the results in Table A with results using the same temperature and ratio of HF to CH2CI2 in Table 2 illustrates the superior results obtainable with low-ash content carbon. Comparison of the results in Table A with results using the same temperature and HF to CH 2 CI 2 in Table 1 illustrates superior results using low-ash content 15
• a quartz tube was charged with 400 g of Carbon A.
• the carbon was washed with de-ionized water at a flow rate of 40 mL/min at room temperature for 72 hours.
• the carbon granules were then dried at 150°C for 60 hours in air to obtain 373 g of dried granules.
• the ash content of this water washed carbon was about 1 weight percent.
• a solution of CrCl 3 *»6H 2 ⁇ (3.15 g) in de-ionized water (50 mL) was prepared in a round-bottomed flask. To this solution was added a portion (25.0 g) of the water washed carbon prepared as described above.
• the slurry was stirred on a rotary evaporator at room temperature at ambient pressure for 2 hours. The water was then removed under vacuum and the granules dried at 130°C in nitrogen for 20 hours. The recovered catalyst weighed 26.65 g and contained about 7.5 weight percent CrCl 3 . Flugrination The reactor was charged with a 7.5% CrCl 3 on water washed Carbon A (15 mL, 6.92 g) catalyst prepared as 16
• the reaction temperature was varied from 200 to 300°C
• the molar ratio of HF to CH 2 CI2 was varied from 2:1 to 4:1 and the contact time was 15 seconds in all cases.
• the CH 2 CI 2 feed to the reactor contained 98.7% CH 2 CI2 and 1.3% CH 2 CIF.
• the reaction effluent was analyzed according to the Analytical Procedure above. The reaction results are shown in Table B. Comparison of the results in Table B with results in Table 1 and Table 2 illustrate the superior results obtainable using low-ash content carbon in accordance with this invention.
• the reactor was charged with a 10% CrCl 3 on HC1- washed Carbon B (15 mL, 6.5 g) catalyst and the catalyst was activated according to the Activation Procedure above.
• the reaction temperature was varied from 200 to 250°C
• the molar ratio of HF to CH 2 CI 2 was varied from 1:1 to 2:1 and the contact time was varied from 5 to 15 seconds.
• the CH 2 CI 2 feed to the reactor contained 98.9% CH 2 CI 2 and 1.1% CH2CIF.
• the reaction effluent was 17
• the reactor was charged with a 20% CrCl 3 on HC1- washed Carbon B (15 mL, 6.6 g) catalyst and the catalyst was activated according to the Activation Procedure above.
• the reaction temperature was varied from 185 to 250°C, the molar ratio of HF to CH 2 CI 2 was varied from 1.5:1 to 2:1 and the contact time was varied from 5 to 15 seconds.
• the CH 2 CI 2 feed to the reactor contained 98.9% CH 2 CI2 and 1.1% " CH 2 C1F.
• the reaction effluent was analyzed according to the Analytical Procedure above. The reaction results are shown in Table 4.
• the reactor was charged with a 60% CrCl 3 on HC1- washed Carbon B (15 mL, 9.0 g) catalyst and the catalyst was activated according to the Activation Procedure above.
• the reaction temperature was varied from 150 to 200°C, the molar ratio of HF to CH 2 CI 2 was 2:1 and the contact time was 15 seconds.
• the CH 2 CI 2 feed to the reactor contained 98.9% CH 2 CI 2 and 1.1% CH 2 C1F.
• the reaction effluent was analyzed according to the Analytical Procedure above. The reaction results are shown in Table 5.
• the reactor was charged with a 7.5% CrCl 3 on HC1- washed Carbon B (15 mL, 6.22 g) catalyst and the 5 catalyst was activated according to the Activation Procedure above.
• the reaction temperature was varied from 275 to 350°C, and the contact time was varied from 5 to 15 seconds.
• the organic feed to the reactor consisted of 81.3 mole % CH 2 CI 2 and 18.2 mole % CCI 3 CF 3 0 with the rest consisting essentially of 0.4 mole %

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• 1993
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